1. Field of the Invention
The invention relates to a pivotal device of a vehicle seat. More particularly, the invention relates to a pivotal device of a vehicle seat, which connects two members that constitute the vehicle seat such that the two members are rotatable relative to each other, and has a function of locking or inhibiting rotation of the two members.
2. Description of Related Art
A known example of pivotal device (reclining device) that connects a seat back of a vehicle seat with a seat cushion such that the angle of the seat back relative to the seat cushion is adjustable is disclosed in Japanese Patent Application Publication No. 2008-506481 (JP 2008-506481 A). The reclining device has a disc-shaped ratchet joined integrally to the seat back, and a disc-shaped guide joined integrally to the seat cushion, and the ratchet and the guide are assembled together in the axial direction to be rotatable relative to each other, and are prevented from being detached from each other in the axial direction by a ring-shaped outer holding member mounted over the outer peripheries of the ratchet and the guide.
The ratchet and the guide are locked, or inhibited from rotating relative to each other, when pawls set on the guide and having external teeth are moved radially outward so as to mesh with internal teeth formed in a radially outer portion of the ratchet. More specifically, the pawls are provided at two or more positions in the circumferential direction of the guide, and one of the pawls is divided into two or more parts at an oblique angle(s) with respect to the circumferential direction. As the pawl is pushed outward in a radial direction of the ratchet, the width of the pawl as measured in the circumferential direction increases, so that clearances between the pawl and the guide in the circumferential direction are eliminated, and the pawl is brought into meshing engagement with the inner teeth of the ratchet with no clearances left between the pawl and the guide. As a result, the ratchet and the guide are placed in the locked state in a condition where they are inhibited from moving relative to each other in the circumferential direction.
Although the ratchet and the guide are inhibited from moving relative to each other in the circumferential direction according to the technology disclosed in JP 2008-50641 A, relative movement of the ratchet and the guide in radial directions due to clearances formed between the ratchet and the guide upon mounting thereof cannot be prevented.